This invention relates to a rugged, high strength, submersible electrical cable and connector assembly particularly suitable for use with solenoid-operated valves for actuating air guns in marine seismic surveying.
In accordance with such applications, the invention relates to an electrical cable and connector assembly which is submersible in salt water and in other aspects relates to such an assembly which is capable of withstanding large vibrational forces associated with the firing of air guns as well as other forces such as the stresses of towing long lengths of cable through a body of water.
Seismic energy sources, commonly referred to as air guns, are utilized in marine seismic surveying to generate powerful seismic impulses by releasing high pressure air and other gases in an abrupt and repeatable manner at short spaced intervals at selective depths within a body of water, within a bore in the earth, or within a confined volume of water above a diaphragm pressing the earth surface. The magnitude of the seismic energy impulses generated are large as the guns usually employ air pressures of several thousand pounds per square inch. Solenoid-operated valves for triggering the release of the high pressure air from the air guns are remotely controlled from a ship or other surface installation. Accordingly, an electrical cable and connector assembly must be able to function reliably in the face of the large vibrational forces generated by firing of the air gun as well as being able to withstand the towing stresses in the water through which the cable extends as the air gun is being towed during a seismic survey operation at sea.
U.S. Pat. No. 3,588,039 entitled "Solenoid Valve Structures and Systems", which is assigned to the assignee of the present invention, illustrates a high tensile strength electrical cable and connector system which has been successfully employed in seismic surveying applications. The electrical cable contains a central flexible stranded stainless steel cable which is mechanically fastened in the connector assembly to a steel anchor plug positioned in a sleeve body member of the connector system. Insulated electrical conductors are helically wound around the stranded steel cable and extend through passages in the metallic anchor plug and are connected to electrical sockets positioned in an end piece of the connector assembly. Although such an arrangement has proven suitable, it has several disadvantages.
First of all, it requires a strengthening steel cable running axially through the electrical cable which performs only a mechanical function of withstanding towing stresses. The electrical conductors which perform the control function are helically wound around the steel cable core, and accordingly they are positioned close to the perimeter of the cable. In other words, the insulated electrical wires are positioned relatively far from the axis of the over-all cable and accordingly they are placed under greater stress than would be the case were they located more centrally in the cable in the space taken up by the steel cable core.
Secondly, the insulated electrical conductors must extend through openings in the steel anchor plug and may become short circuited if the insulation thereon is damaged by the plug due to the large vibrational forces which are applied to the assembly by the repeated firings of the air gun.
Third, the prior art cable is relatively bulky because the steel cable core increases its over-all diameter, and then the electrical conductors must be well insulated from this steel core as well as being well insulated from the surrounding sea water or other environment, which further increases the bulk of the composite cable. The present invention is directed to a new and improved structure which alleviates these as well as other problems with respect to the electrical cable and connector assembly.